Prague used to be known with bad taxi drivers. Some of them were real bandits and were even involved with crime. But it has been improving in last few years and now you don't have to worry about calling taxi through the operator anymore. One of the best is AAA Taxi, they are not expensive and the operators speak English, just dial 14014. On the contrary hailing taxi on the street is still hazardous and we can't recommend it.

Cited from the CzechSite

Whether you land at Prague aiport or get off your train at the station, the safest and cheapest way is to buy a phone card at a newsstand (at 150 CZK) and call AAA taxi from the nearest phone booth. Phone numbers are 14014 or 3311 3311 or 333 22 333. The taxi will arrive in a while, they are waiting nearby but do not fight with gangs that occupy lucrative posts.

Be sure you recover the cost of the phone card just by the ride from the airport to downtown.

Crime